Thickness sensor for conductive features

Abstract

Various embodiments provide a thickness sensor and method for measuring a thickness of discrete conductive features, such as conductive lines and plugs. In one embodiment, the thickness sensor generates an Eddy current in a plurality of discrete conductive features, and measures the generated Eddy current generated in the discrete conductive features. The thickness sensor has a small sensor spot size, and amplifies peaks and valleys of the measured Eddy current. The thickness sensor determines a thickness of the discrete conductive features based on a difference between a minimum amplitude value and a maximum amplitude value of the measured Eddy current.

What is claimed is: 
     
       1. A device, comprising:
 an Eddy current reader configured to measure Eddy currents induced in a plurality of conductive features on a substrate, and generate an Eddy current signal based on the measured Eddy currents; and 
 a processor configured to calculate a thickness value representing a thickness of the conductive features based on a difference between a maximum amplitude value of the Eddy current signal and a minimum amplitude value of the Eddy current signal. 
 
     
     
       2. The device of  claim 1  wherein the plurality of conductive features are electrically isolated from each other. 
     
     
       3. The device of  claim 1 , further comprising:
 a sensor coil configured to sense a magnetic field generated by the Eddy currents, the Eddy current reader measures the Eddy currents based on the magnetic field. 
 
     
     
       4. The device of  claim 1  wherein the processor calculates the thickness value concurrently with a chemical mechanical polishing (CMP) process. 
     
     
       5. The device of  claim 4 , further comprising:
 a polishing module configured to adjust the CMP process based on the thickness value. 
 
     
     
       6. The device of  claim 1  wherein the processor is configured to calculate a density value representing a density of the conductive features based on the difference. 
     
     
       7. A device, comprising:
 an Eddy current reader configured to measure Eddy currents in a plurality of conductive features on a substrate, and generate an Eddy current signal based on the measured Eddy currents; and 
 a processor configured to receive the Eddy current signal, determine a maximum amplitude value of the Eddy current signal, determine a minimum amplitude value of the Eddy current signal, and calculate a thickness value representing a thickness of the conductive features based on the maximum amplitude value and the minimum amplitude value. 
 
     
     
       8. The device of  claim 7  wherein the processor is configured to calculate a difference between the maximum amplitude value and the minimum amplitude value, and calculate the thickness value based on the difference. 
     
     
       9. The device of  claim 7  wherein the plurality of conductive features are electrically isolated from each other. 
     
     
       10. The device of  claim 7 , further comprising:
 a driver configured to generate a driving signal; 
 a drive coil configured to receive the driving signal, and induce the Eddy currents in the plurality of conductive features in response to the driving signal being received; and 
 a sensor coil configured to sense a magnetic field generated by the Eddy currents, the Eddy current reader measures the Eddy currents based on the magnetic field. 
 
     
     
       11. The device of  claim 10  wherein the drive coil has a first diameter, and the sensor coil has a second diameter that is smaller than the first diameter. 
     
     
       12. The device of  claim 10  wherein the drive coil has a first diameter, and the sensor coil has a second diameter that is substantially equal to the first diameter. 
     
     
       13. The device of  claim 7 , further comprising:
 a polishing module configured to perform a polishing process, and stop the polishing process based on the thickness value. 
 
     
     
       14. A device, comprising:
 an Eddy current reader configured to measure first Eddy currents in a first plurality of conductive features, and generate a first Eddy current signal based on the measured first Eddy currents; and 
 a processor configured to determine a reference amplitude value based on a minimum amplitude value of the first Eddy current signal, and calculate a thickness value representing a thickness of the first plurality of conductive features based on the reference amplitude value. 
 
     
     
       15. The device of  claim 14  wherein
 the Eddy current reader is configured to measure second Eddy currents in a second plurality of conductive features, and generate a second Eddy current signal based on the measured second Eddy currents, and 
 the processor is configured to update the reference amplitude value based on a minimum amplitude value of the second Eddy current signal, and calculate a thickness value representing a thickness of the second plurality of conductive features based on the updated reference amplitude value. 
 
     
     
       16. The device of  claim 14  wherein the processor is configured to calculate a difference between a maximum amplitude value of the first Eddy current signal and the reference amplitude value, and calculate the thickness value based on the difference. 
     
     
       17. The device of  claim 14  wherein the first plurality of conductive features are electrically isolated from each other. 
     
     
       18. The device of  claim 14 , further comprising:
 a driver configured to generate a driving signal; 
 a drive coil configured to receive the driving signal, and induce the first Eddy currents in the first plurality of conductive features in response to the driving signal being received; and 
 a sensor coil configured to sense a magnetic field generated by the first Eddy currents, the Eddy current reader measures the first Eddy currents based on the magnetic field. 
 
     
     
       19. The device of  claim 14  wherein the processor calculates the thickness value concurrently with a chemical mechanical polishing (CMP) process. 
     
     
       20. The device of  claim 14 , further comprising:
 a polishing module configured to perform a polishing process, and adjust the polishing process based on the thickness value.